1. Technical Field
This disclosure relates to the fabrication of magnetic read/write heads that record at high data rates. More particularly, it relates to such a structure that incorporates a main writing pole that is activated inductively by a vertical coil.
2. Description
With growing demands for cloud storage and cloud-based network computing applications, high and ultra-high data rate recording becomes important for high-end disk drive applications. It is essential to design perpendicular magnetic recording (PMR) writers that can achieve such optimum high data rate performance.
Referring to FIG. 1, there is shown schematically a vertical (x-direction) cross-sectional view (x-z plane) of a PMR writer with a pancake (flat) coil design. The ABS plane of the writer (1) is the x-y plane. The plane of the pancake coil is the y-z plane. The y-axis is the cross-track direction and the x-axis is the down-track direction.
The PMR writer includes a main pole (4), denoted MP, with a small surface area at its tip, which emerges at the ABS plane (1). A trailing shield (6), also denoted PP3, serves to channel the flux that emerges from the main pole and passes through the recording medium back through the writer to complete the induced flux loop. The MP and the PP3 are connected together by a yoke (5), denoted TY. The PP3 is also coupled at its ABS end to a write shield (7), which we will denote as WS, to enhance the flux intensity and shield other portions of the writer from its flux. The magnetic flux that emerges from the MP (4) is generated by a driving coil (3a & 3b). The driving coil is shown in cross-section as three rectangles (3a) on the ABS side of the TY and three rectangles (3b) on the opposite side of the TY. These rectangles are the plane cross-sections through the coil. The driving coil is a horizontal, planar spiral, i.e., a “pancake,” with its continuous coil turns being wound about the TY. A bucking coil (2a & 2b), is like a mirror image of the driving coil and is formed beneath the driving coil The driving coil is wound in series with the bucking coil, but is wound in an opposite direction, and the two coils are connected through a connector (8). The purpose of the bucking coil is to minimize the inductive coupling between the current in the coils and PP3. The yoke length of the writer configuration is defined as the distance from the ABS (1) to point A, which is at the inner corner where PP3 (6) joins the TY (5).
Referring next to FIG. 2, there is shown a schematic illustration, in a top view (y-z plane), of the spiral configuration that forms either (3a) and (3b) of FIG. 1. Note that the spiral turns are narrow and compressed at the ABS end (3a), so they can fit within the confines of the writer that is defined by the yoke length. The configuration is denoted as having 3+3 turns, (3+3)T, to indicate the three turns of the driving coil and the three turns of the bucking coil.
For a write head to operate at high speed, three issues must be addressed: intrinsic yoke flux response; write current response and magnetization current response. Short yoke length (SYL) and narrow main pole and yoke width have been identified as key dimensions for improved data rate performance because they can reduce eddy current damping and improve intrinsic yoke flux response. As yoke length is reduced, coil height and width must shrink in order to fit into the reduced available space. As a result of this reduction in coil size, the coil resistance increases. High coil resistance is not desirable as Joule heating of the coil by the write current (Iw) may induce large write pole tip protrusion (IwPTP) caused by thermal expansion. As writing frequency increases, Joule heating also increases in proportion to the frequency. The challenge then becomes: how to reduce coil resistance without any penalty to high data rate performance, or to even gain high data rate performance. These issues have been addressed in various ways by Khizroev et al (U.S. Pat. No. 6,876,518), Wang et al. (U.S. Pat. No. 7,102,854), Shukh et al. (U.S. Pat. No. 6,477,007), Golgolab et al. (U.S. Pat. No. 7,505,231), Huang et al. (U.S. Pat. No. 8,081,401). Additional background material is found in J. Jury et al. “Design of a single turn microstrip write head for ultra-high data rate recording” IEEE Trans. On Magnetics, Vol. 35, No. 5, September 1999. However the approaches advocated in these teachings do not deal with the challenges in the manner to be discussed herein nor do they obtain results that offer such significant improvements.